cvs commit: src/lib/libc/sys chown.2

[Bruce Evans]

On Wed, 13 Dec 2006, Pawel Jakub Dawidek wrote:

> pjd         2006-12-13 11:46:38 UTC
>
>  FreeBSD src repository
>
>  Modified files:
>    lib/libc/sys         chown.2
>  Log:
>  Be more precise with EPERM description. When chown(2) is a no-op, it will
>  return 0.

VADMIN access is still required for null changes.  This normally means
that the the caller must own the file, but there are complications for
ACLs.  Also, non-null changes within the group don't require super-user
permissions.
The details for this are hard to describe. They are at least as complicated
as:
- the effective uid must be the super-user, unless all of the following:
   . it is the same as the file's uid, or [complications for ACLs]
   . the change to the uids of the file is null
   . [permission is never granted based solely on the egid-- check this]
   . the change to the gids is either null or the new file gid is in the
     same group as the egid.
   . [nothing is required or the old file gid -- check this]
I used fine print in POSIX to justify permitting null changes to the
gid.  FreeBSD-1 doesn't allow this.  My reasoning was something like
"non-null changes (from a gid not in our group to one in our group)
are permitted (if euid == old file uid == new file uid), so why disallow
null changes?  The uid checks should be sufficient."  McKusick agreed
with this.

All this is mainly for ffs.  Many file systems are probably still
stricter.  Some non-POSIX ones should be less strict when they only
have fake attributes and the fake attributes get in the way of making
null changes.

Sorry I didn't update the man page or all file systems for this.

A previous change to chown.2 copied bad grammar (a comma splice) from
somwhere.  Grep for "more info" in *.2 to see some good and bad examples.
intro.2 uses a semicolon splice, but using a new sentence seems to be
most common.  The wording in examples with correct grammar also tends
to be more formal (a bit too formal/verbose for me).

Bruce